Industrial Application Areas
This invention relates to an impact-resistant polystyrene resin composition offering a well-balanced combination of impact strength and gloss.
Rubber-modified polystyrene has widely been used in components of domestic electric appliances and other like appliances. However, this material is inferior to the conventional ABS resin in relation to gloss and impact strength of finished products. Another drawback has been its poor colorability. Recently, there has been a growing demand for rubber-modified polystyrene that would compare favorably with ABS resin from the standpoint of cost and applicability to the thin-walled products.
The resin composition of the present invention excels in gloss, impact strength, and rigidity. Thus, the resin composition of the present invention enables the production of injection-molded products, extruded sheets, and vacuum-formed products with high impact strength and good gloss, which are comparable to those obtained by using expensive ABS resin. Thus, it can be of considerable value as an economical resin.
Related-Art Statement
Rubber-modified polystyrene has been widely used in the industry for a long period of time. Normally the rubber particle size dispersed is polystyrene matrix is about 1.0-5.0 microns. Recently, to achieve high gloss in molded products, rubber-modified polystyrenes with a smaller rubber particle size have been developed and introduced to the market. However, products with 1.0 micron or less in rubber particle size is characterized with a substantially low impact strength, and for this reason, desirable resins have not yet been obtained from these products. Further, to improve the balance of impact strength and gloss, a composition comprised of a blend of rubber-modified polystyrene containing rubber particles less than 1.0 micron in particle size and those containing larger rubber particles, have been disclosed in existing literature, such as Japanese Patent Publication B46-41467, Japanese Patent Publication B59-1519, U.S. Pat. No. 4,146,589, U.S. Pat. No. 4,214,056, and U.S. Pat. No. 4,493,922. However, the large particles used in these prior art were of 2 microns or greater. These large particles gave low surface gloss of the molded article (In particular, those large particles gave a large "gloss gradient, " which means the gloss value of the parts in the molded articles which are further from the injection gate have a sharply lower gloss, as compared with the parts which are near the gate). Also, when these products are molded under a low mold temperature, the gloss markedly decreased.
Other, resin compositions made of rubber-modified styrene resin and organic polysiloxane have been disclosed in existing literature such as Modern Plastics, November 1972, pp. 114-115; Plastics Age, 1974, Vol. 20, May, p. 107; Japanese Patent Laid-Open A55-3494; Japanese Patent Laid-Open A53-124561; Japanese Patent Laid-Open A57-172948; Japanese Patent Laid-Open A57-187345; and Japanese Patent Laid-Open A57-187346. However, such mixtures, in which rubber-modified polystyrene in which a small rubber particle size is used, have not yielded a resin composition with desirable properties.
Further, another resin compositions made of rubber-modified polystyrene resin, polydimethylsiloxane, and metallic salts of higher fatty acids are disclosed in Japanese Patent Laid-Open A61-183339; and those comprised of rubber-modified styrene resin, polydimethylsiloxane, and amides of higher fatty acids are disclosed in Japanese Laid-Open A61-183341. These products also have not yielded a resin composition with desirable properties when used in conjunction with rubber-modified polystyrene with a small rubber particle size.
To meet the market demand for rubber-modified polystyrene with a well-balanced combination of properties, as noted above, it is necessary to produce a rubber-modified polystyrene resin with a well-balanced combination of properties such as good surface gloss (especially a high gloss value and a small gloss gradient) in molded products, high impact strength, and high rigidity.